One of the representative methods for various color recording methods may be a recording method using an ink jet printer, that is, an ink jet recording method. This recording method involves producing small droplets of ink, and attaching these small droplets to various record-receiving materials (paper, film, clothes and the like) to perform recording. In this method, the method is characterized in that since the recording head and the record-receiving material are not brought into direct contact, the process is quiet with less noise generation, and size reduction or an increased speed can easily be achieved. Therefore, the method has rapidly become popular in recent years, and an extensive growth in use of the method is expected.
Conventionally, aqueous inks prepared by dissolving a water-soluble coloring matter in an aqueous medium have been used as the inks for fountain pens, felt pens and the like and as the inks for ink jet recording. In these aqueous inks, water-soluble organic solvents are generally added so as to prevent clogging of the inks at the pen tips or ink discharge nozzles. Furthermore, these inks are required to have advantages such as the production of recorded images of sufficient densities, no occurrence of clogging at the pent tips or nozzles, satisfactory drying properties on record-receiving materials, less bleeding, and excellent storage stability. Also, the water-soluble coloring matters used therein is required to have high solubility particularly in water, and high solubility in the water-soluble organic solvents that are added to the ink. In addition, the images thus formed are required to have various image fastness properties such as water resistance, light fastness, gas fastness and moisture resistance. Furthermore, development of a coloring matter producing high recorded images is required.
Among these, the above-described term gas fastness is a resistance to the phenomenon that oxidizing gas such as ozone gas present in air acts on the coloring matter within a recording paper and changes the color of a printed image. In addition to ozone gas, examples of oxidizing gases having this kind of action include NOx and SOx. However, among these oxidizing gases, ozone gas is considered as a main causative substance which accelerates the phenomenon of discoloration and fading of ink jet recorded images. For this reason, among the gas fastness, particularly ozone gas fastness tends to be regarded as most important. In an ink-receiving layer provided on the surface of exclusive ink jet paper of photographic image quality, materials such as porous white inorganic substances are frequently used for the purpose of speeding up drying of the ink, and reducing the bleeding at high image quality. In the images recorded in such a recording paper, significant discoloration and fading of the recorded image due to ozone gas is observed. Since the phenomenon of discoloration and fading due to an oxidizing gas, is characteristic to ink jet images, an enhancement of ozone gas fastness has been one of the most important problems to be solved in the ink jet recording method.
Indicators for deterioration of recorded images to light are divided broadly into 2 kinds of indicators. One is those using the degree of decline of print density of recorded images as an indicator, and the other one is those using the degree of change of the hues of recorded images as an indicator. The decline of print density is observed as the fading of recorded images, and the change of the hues is observed as the color change of recorded images.
In order to store recorded images in the state of high quality for a long time, it is required to develop a coloring matter that is hard to have occurrence of the decline of the print density and the change of the hues to light, and is excellent in light fastness.
It is known that a coloring matter producing high recorded images is used to obtain recorded images having high quality of further density feeling. Additionally, it is possible to solve nozzle clogging when printing with an ink jet printer.
The nozzle clogging of an ink jet printer is often derived from the fact that the moisture in the ink in the vicinity of the nozzles is evaporated earlier than other solvents or additives, and coloring matters are solidified and precipitated when the ink comes to have a composition state where the moisture is less and the solvents or the additives are more. As a method for solving the nozzle clogging, a technique of using a coloring matter having high print density is known. Use of the coloring matter having high print density makes it possible to lessen the solid content of the coloring matters in the ink while maintaining conventional print density. This makes it difficult for the coloring matters to be precipitated, and also is advantageous in terms of the cost, and a coloring matter having high print density is desired to be developed.
In order to expand the field of use in those recording (printing) methods using ink in the future, it is strongly desired to enhance light fastness, ozone gas fastness, moisture resistance and water resistance and to further enhance color development properties in the ink composition used in ink jet recording and the colored body colored by the ink composition.
Inks of various colors have been prepared from various coloring matters; however, among them, a black ink is an important ink that is used in both of mono-color and full-color images. However, it has many difficult points technically to develop a coloring matter having a neutral hue between the dark color gamut and the light color gamut, and having high print density, and further having less dependency of the hue on the light source and exhibiting good black. Thus, although many researches and developments have been performed, those having sufficient performances are still few. Thus, it is generally performed to prepare a black ink by combining multiple, versatile coloring matters. However, the preparation of an ink by mixing multiple coloring matters has problems such as 1) variation of the hues depending on the medium (record-receiving materials) and 2) particularly, increase of discoloration by decomposition of the coloring matters by light or ozone gas, in comparison to adjustment of an ink with a single coloring matter.
A black ink composition for ink jet to render a printed matter to have good various durabilities is proposed in, for example, Patent Documents 1, 2 and 3, and the like. This ink composition is a greatly improved ink composition having good image fastness properties of a printed matter. However, use of these ink compositions as an ink in a single color has not been applied to a neutral black printed matter, and have not sufficiently satisfied further demands of the market requiring high image fastness properties. In addition, Patent Documents 4 and 5 disclose a technique of combining various inks to obtain a black ink composition. However, there is no disclosed ink composition satisfying high fastness properties and color development properties, whereby to satisfy demands of the market.    Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2009-84346    Patent Document 2: PCT International Publication No. WO2009/069279    Patent Document 3: PCT International Publication No. WO2005/097912    Patent Document 4: PCT International Publication No. WO2007/077931    Patent Document 4: Japanese Translation of PCT International Publication, Publication No. 2009-512737